What is the function of the varistor?

Varistors are used to protect a circuit from high voltage surges. When a high voltage surge is applied to a circuit, the outcome is usually catastrophic to the circuit. A capacitor may be installed across the signal lines.

How do you identify varistors?

While it may look similar to a capacitor, you can identify the device by its color, markings and location. The MOV will always be close to the equipment’s power supply and wired to a fuse. Many MOVs have a bright, solid color and are usually coin-sized. Unplug the equipment from the electrical outlet.

What do the numbers on a varistor mean?

The energy rating for the varistor is often defined using standardised transients. The transient is expressed in the format x/y where x is the time for the transient rise and y is the time to reach its half peak value. Typical formats are 8/20 and 10/1000.

How do you test for a bad varistor?

Touch one meter probe to the free varistor lead and the other probe to the connected lead. Read the resistance on the meter. If it reads nearly infinite resistance, the varistor is still good. If it reads very low resistance, the varistor is blown.

Why would a varistor burn out?

When the varistor leakage current is too large, and the temperature rises to a certain extent, the low melting point metal is melted, thereby varistor from The cutting in the circuit can effectively prevent the varistor from burning.

Can you remove a varistor?

Simply remove it untill you find a replacement. The circuit will work without it.

What is the difference between thermistor and varistor?

A varistor is essentially an open circuit until its breakdown voltage is exceeded which point it begins its resistance drops steeply. A thermistor is more of a temperature sensitive resistor; it’s not “normally closed”, it’s a resistor.

Do varistors go bad?

After prolonged use they can degrade and the material that makes up the disc can start a leakage current due to internal damage after a surge event, this will create a higher leakage current over time and before you know it we have a thermal runaway event.

What are the main parameters of a varistor?

The main parameters of the varistor are nominal voltage, voltage ratio, maximum control voltage, residual voltage ratio, discharge current capacity, leakage current, voltage temperature coefficient, current temperature coefficient, voltage nonlinear coefficient, insulation resistance, static capacitance and so on.

Which is a surface mountable varistor ( MOV ) device?

Surface mountable MOV (Metal Oxide Varistor) devices facilitate customs in SMT assembly process and resolve the PCB space limitation issue. They are reflow and wave solderable and include the CH, SM7, SM20, MLE, MHS, ML, and MLN series.

How are varistors considered to be multi junction devices?

Since the nonlinear electrical behavior occurs at the boundary of each semiconducting ZnO grain, the varistor can be considered a “multi-junction” device composed of many series and parallel connections of grain boundaries. Device behavior may be analyzed with respect to the details of the ceramic microstructure.

How is a metal oxide varistor ( MOV ) made?

The Metal Oxide Varistor or “MOV” is sintered during the manufacturing operation into a ceramic semiconductor and results in a crystalline microstructure that allows MOVs to dissipate very high levels of transient energy across the entire bulk of the device.